diff --git a/rtcclient/workitem.py b/rtcclient/workitem.py
index d52d0cf..08a31d3 100644
--- a/rtcclient/workitem.py
+++ b/rtcclient/workitem.py
@@ -608,7 +608,10 @@ def _addChildren(self, child_ids):
 
         # retrieve current children
         cur_children = self.getChildren(returned_properties="dc:identifier")
-        cur_child_ids = [cur_child.identifier for cur_child in cur_children]
+        if cur_children:
+            cur_child_ids = [cur_child.identifier for cur_child in cur_children if cur_child]
+        else:
+            cur_child_ids = []
 
         # add current children to list
         for child_id in cur_child_ids: